In future mobile systems, the proportion of a radio resource to be allocated to different subscribers varies considerably according to the required capacity and the standard of service. The new services offered together with normal speech transmission and the requirements relating to data transmission increase the need for allocating the radio resource more efficiently.
A frequency band reserved for a radio system is allocated to users as radio channels in accordance with the selected multiple access technique (Multiple Access). A radio channel is a frequency band employed in a radio connection or a portion of the frequency band separated for example by means of time or a user-specific code. In analogue systems, radio channels are usually frequency channels, whereby a dedicated frequency band is reserved for each radio connection, the frequency band being a part of the frequency resource in the system. This technique is called frequency division multiple access (FDMA). In time division multiple access (TDMA), a time slot is assigned for each radio connection from a common frequency band. Code division multiple access (CDMA) is a multiple access technique implemented by means of a spread spectrum technique wherein radio transmissions employing the same frequency band are coded in such a way that signals for a particular receiver party can be received only at particular receivers.
A radio system based telecommunication connection can be a simplex or a duplex connection. The simplex connection is a telecommunication connection wherein the user can only either transmit or receive information simultaneously. The duplex connection is a telecommunication connection wherein the user can transmit and receive information simultaneously. A semiduplex connection is a combination of the two aforementioned connections, i.e. a telecommunication connection wherein one party employs the simplex connection and the other party employs the duplex connection.
In radio traffic, the duplex connection is often implemented by employing different transmission and reception frequencies (frequency division duplex, FDD). The difference between the transmission frequency and the reception frequency is called a duplex spacing. Most digital mobile communication systems, such as the GSM (Global System for Mobile Communications) and DCS-1800 (Digital Cellular System for 188 MHz) are based upon time division multiple access (TDMA) implemented by a FDD telecommunication connection. New PCS (Personal Communication System) systems implemented in the U.S. will apply a new IS-95 system based upon code division multiple access (CDMA).
Another duplexing method is time division duplex (TDD) wherein the signals are transmitted time-interleaved on the same transmission channel. In systems employing frequency division multiple access (FDMA) implemented by a TDD telecommunication connection, for example in the CT2 (Cordless Telephone, 2nd generation), transmission alternates with reception in a frequency band reserved for one subscriber. In systems employing time division multiple access (TDMA) implemented by the TDD connection, such as the DECT (Digital European Cordless Telecommunications), transmission alternate with reception in a frequency-band time slot reserved for one subscriber.
In mobile communication systems, the connection between mobile stations and base stations is accomplished through a radio path. A channel from the mobile station to the base station is called an uplink transmission path and, correspondingly, a channel from the base station to the mobile station is called a downlink transmission path.
A radio connection is based on successive data frames, the data frames being constructed according to the selected multiple access technique of for example adjacent frequency bands and time periods. The part of the frame which can be unambiguously referred to by means of selected parameters (such as a frame frequency band, a time slot number or a code) is called a frame address. A radio channel is hereinafter taken to mean a data transmission implemented in adjacent frames in one or several determined frame addresses. The properties of the radio channel communication can be affected by allocating the frame addresses. By establishing a radio channel composed of several frame addresses, more data transmission capacity will be obtained for example for the data transmission.
An interactive data transmission is a duplex communication where messages in the uplink and downlink transmission paths interact with each other. An example is given here illustrating a channel allocation between the mobile station and the base station. The uplink transmission path is hereinafter referred to as the uplink and the downlink transmission path is referred to as the downlink. The base station informs about free addresses a message transmitted on a Y channel (Yell) in the downlink direction. A mobile station desiring to establish a connection transmits a random access (RA) message in the uplink direction on a channel selected among the channels indicated to be free by the Y channel, the RA message including the desire to establish a connection. The desired standard of service, i.e. the amount of the resource the connection to be established requires, is also informed in the RA message. The RA message is responded by an access grant (AG) message in the downlink direction, the AG message informing the mobile station about the frame address or frame addresses to be employed in the radio channel to be established.
The above described message transmission is accomplished without problems when traffic intensity is low enough, the downlink messages having enough time to react with the previous uplink messages by means of the suitable selection of the frame addresses. The frame becomes full with the increase of traffic, whereby the messages relating to the interactive connection are located within the entire frame matrix and all the message addresses cannot then be selected in a suitable way. Consequently, the downlink messages cannot always be positioned in such frame addresses wherein the messages would have enough time to react with the messages submitted in the previous message in the uplink direction or, on the other hand, where there would be enough time to transmit information useful for all the subsequent frames in the uplink direction. The use of the channel resources in this way is ineffective and radio spectrum is wasted in the implementation of the interactive connection.
A similar problem is faced for example with the data transmission originating from the mobile station in connection with acknowledgement messages. A number of frame addresses is allocated to a subscriber for the data transmission. When the data transmission in the uplink direction is completed, the base station sends an acknowledgement message (for example automatic repeat request, ARQ) to the mobile station, the subscriber using the message for detecting whether the data transmission was successful. If the system disconnects the connection immediately after the data transmission and, after disconnecting the connection, receives a message of the data transmission failure, the connection must be re-established. If the system maintains the connection until the positive acknowledgement, an extensive channel allocation must be maintained unnecessarily in connection with the positive acknowledgement, i.e. capacity is wasted in the implementation of the interactive message transmission.